For example, what is called “hardening” aiming at raising mechanical strength etc. of a “tubular member having a bend portion” (which may be referred to as a “bent pipe” hereafter) used as a part for a vehicle, such as a door impact beam and an antiroll bar, has been known. A hardening treatment is a treatment in which a member as a treatment target is heated to a predetermined temperature or higher and thereafter cooled rapidly. The hardening treatment may be performed on the whole member as the treatment object, or it may be performed locally on a part of the member as the treatment object.
As a specific example of the former, for example, it has been known to rapidly cool a pipe subjected to bending beforehand (bent pipe) (by making the pipe contact with cooling water, etc.) after heating the whole pipe to a predetermined hardening temperature or higher. However, in accordance with this method, since a hardening treatment is performed to the whole bent pipe, this method cannot be applied when a hardening treatment is not performed on a part of a bent pipe, for example.
On the other hand, in the latter case, it is common to perform a hardening treatment on a part of a bent pipe by moving a hardening means including a heating means and a cooling means little by little along a longitudinal direction of a bent pipe to heat and cool a part of the pipe, which needs to be hardened. In this case, on the contrary to the above, the hardening means may be fixed and a bent pipe may be moved. Namely, any of a bent pipe and a hardening means may move, and they just have to move relatively.
In any case, while a bent pipe and a heating means are moving relatively, when a spatial relationship between the bent pipe and the heating means deviates (inclines) or, furthermore, when the bent pipe and the heating means interfere, there is a possibility that a hardening treatment of the bent pipe may become uneven, or the heating means may be damaged. Therefore, the spatial relationship between the bent pipe and the heating means needs to be controlled strictly.
As a specific example of such a hardening treatment, for example, an apparatus which cooperatively controls a plurality of industrial robots to simultaneously perform bending and a hardening treatment of a tubular member (which may be simply referred to as a “pipe” hereafter) has been known (for example, refer to the Patent Document 1 (PTL1)). This apparatus comprises a feed mechanism for a pipe, a first support mechanism to support the pipe while feeding the pipe, a heating mechanism, a cooling mechanism, a second support mechanism to give bending moment to a heated part of the pipe to bend the pipe, and a deformation preventing mechanism for a pipe.
In order to perform bending with sufficient precision in the above-mentioned apparatus to make a pipe into a desired shape, it is necessary to carry out the cooperative control of the operation of three mechanisms, i.e., the above-mentioned feed mechanism, second support mechanism, deformation preventing mechanism for a pipe, strictly. Therefore, when performing a “changeover” for changing a production brand, complicated operations, such as setting of many control items, confirmation and fine control of an operation becomes necessary for each of the above-mentioned mechanisms. Therefore, the above-mentioned apparatus is not suitable for multi-product production.
Furthermore, as mentioned above, since the above-mentioned apparatus needs a plurality of industrial robots and a controller for cooperatively controlling them, etc., it needs a great installation fee, a vast operation space, and large electric power consumption.
In addition, in the above-mentioned apparatus, since a pipe is bent by using softening of the pipe accompanying heating in a hardening treatment, a hardening treatment is certainly performed on a bent part of the pipe (which may be referred to as a “bend part” hereafter). Therefore, when hardening is not needed in the bend part of the pipe, the above-mentioned apparatus cannot be used.
On the other hand, in the art, a hardening apparatus which performs a hardening treatment on a pipe subjected to bending beforehand (bent pipe) has been also known (refer to the Patent Document 2 (PTL2)). This apparatus comprises an induction-heating coil, a multi-axis robot (articulated industrial robot) as a transportation means, which makes a pipe pass through the inside of the induction-heating coil, and a cooling means disposed on a downstream from the above-mentioned induction-heating coil.
In the above-mentioned apparatus, a bent pipe is held by a plurality of clamps attached at a leading end of an arm of the above-mentioned robot and the above-mentioned robot operates such that the bent pipe passes through an induction-heating coil approximately at a center of the coil. On this occasion, the bent pipe is moved in its longitudinal direction with respect to the induction-heating coil and the cooling means while opening and closing these multiple clamps one by one, and a hardening treatment is performed.
In accordance with the apparatus as mentioned above, since a hardening treatment can be performed regardless of a position of the bend part of the bent pipe, problems resulting from simultaneously performing bending and a hardening treatment like the conventional apparatus as previously mentioned can be solved.
However, in the above-mentioned apparatus, it is necessary to teach and adjust an operation of an industrial robot according to a shape of the bent pipe used as a target of a hardening treatment (workpiece). In addition, in the case of a changeover, it is necessary to change a layout of the above-mentioned multiple clamps according to a shape of a bent pipe. Therefore, also in the above-mentioned apparatus, a complicated operation is needed when performing a changeover.
By the way, as mentioned above, it is known that a long member which has a modified cross-section will be used in a structural member which constitutes a body of a vehicle. Specifically, for example, in a center pillar and a cross member, etc., of a vehicle, a long member having a hat-like cross-section, which is formed by press processing of a steel plate is used.
In addition, a “long member” means a member having a shape in which a size of the member in a specific direction is relatively longer as compared with a size of the member in another direction. The above-mentioned specific direction in the member is referred to as a “longitudinal direction”, and the direction which intersects perpendicularly with the “longitudinal direction” is referred as to a “width direction” or “thickness direction.”
As a method for raising mechanical strength of a long member as mentioned above, for example, a method in which the long member is combined with a reinforcement member having high mechanical strength has been known. However, addition of the reinforcement member may lead to problems, such as increase of weight of the member, increase of a manufacturing cost, and complication of a manufacturing process, for example.
Alternatively, a technology in which a long member having a hat-like cross-section is manufactured by what is called “hot-pressing” and thereby the entire of the long member is formed and hardened simultaneously has been also known. In accordance with the technology, the mechanical strength in all the regions of the long member having a hat-like cross-section can be raised and thereby collision security of a vehicle, etc., can be improved, for example. However, as compared with usual pressing (not accompanied by heating), hot-pressing requires a large-scale installation. As a result, for example, there is a possibility to cause problems, such as, not only increase of a manufacturing cost, but also increase of a cost accompanying a changeover.
Therefore, in the art, a technology which raises mechanical strength of a long member having a hat-like cross-section by performing a hardening treatment partially only on a region in the vicinity of a corner part (bending line (edge) part of a steel plate) of a hat-like cross-section (which may be simply referred to as a “corner part region” hereafter) has been known.
In the above-mentioned hardening treatment, a hardening means, which comprises a high-frequency heating coil as a heating means and a cooling jacket as a cooling means arranged on a downstream side of the heating means, is arranged so as to oppose (face) the above-mentioned corner part region. Then, a hardening treatment can be performed only on the corner part region by moving the hardening means and the long member relatively along the longitudinal direction of the long member (refer to the Patent Documents 3 (PTL3)).
However, in hardening methods for a long member having a hat-like cross-section according to conventional technologies including the above, an axis in the longitudinal direction of a workpiece after a hardening treatment may curve (warp). Specifically, the axis in the longitudinal direction may be distorted such that the workpiece becomes convex-like on the back side (namely, a side opposite to a top plate in the hat-like cross-section (which may be referred to as a “concave portion side” or “flange side”).